Cerebrospinal fluid (CSF) and serum samples of 20 young adults (mean age 41 +/- 3.4 yr) with a first episode of stroke were tested for interleukin-2 (IL-2), soluble interleukin-2 receptor (SIL-2R), tumour necrosis factor-alpha (TNF-alpha) and interleukin-1-beta (IL-1 beta) levels. The results were compared to 20 patients who had neurological symptoms without evidence of a neurological disease. Three subgroups were formed according to the aetiological source of the stroke, determined by the neurological examination and evaluation. In 13 patients, the presence of atheromatous carotid plaque or cardiac disease was found. In five of the patients, stroke was the presenting symptom of systemic lupus erythematosus (SLE), which developed during the follow-up period. In two patients, no obvious aetiology could be demonstrated. The SIL-2R level was significantly higher in the CSF of patients who later developed definite SLE (P = 0.001). Other CSF interleukins and all serum interleukin levels were not significantly different in any of the groups. No correlation between albumin quotient and CSF SIL-2R was found. The SIL-2R level in the CSF may be used as a diagnostic tool to differentiate immunologically mediated vascular processes in the CNS from stroke of other origin.